Combinations of graft modified polyethylene and another polyolefin are known. European Patent Applications 0 465 203 and 0 311 860 disclose bicomponent fibers having a polyester or polyamide core and a sheath component consisting of either a blend of graft-modified polyethylene with homo-polyethylene or a copolymer straight-chain low density polyethylene copolymer. Suggested uses are in making carded, heat bonded nonwoven fabric. The ethylene copolymer of EP '860 is defined as consisting of ethylene and at least one member selected from the class consisting of an unsaturated carboxylic acid and a derivative from said carboxylic acid and a carboxylic acid and a carboxylic acid anhydride.
GB-A-2 125 458 discloses a thermally bonded fibrous web consisting essentially of a bicomponent fiber comprising a polyester or polyamide component and a second component consisting essentially of a linear low density polyethylene having a density in the range of 0.910 to 0.940 g/cc. The web may also include a matrix fiber. Bicomponent fibers having a core of PET and a sheath of a blend of a polyolefin homopolymer and graft-modified polyethylene are commercially available from Hoechst Celanese Corp. under the CELBOND trademark, for example CELBOND T-255.
Experience has shown that core-sheath adhesion is a problem with bicomponent fibers of a PET core/polyolefin sheath. This is not surprising since polyethylene and PET are mutually incompatible.
More specifically, experience with a bicomponent staple fiber of LLDPE-sheath/PET-core configuration has shown shedding of the outer portion of the fiber apparently due to action of the carding wires when processed on carding machines.
There remains a need to develop a staple fiber useful for thermally bonded fibrous webs providing an improved heat fusible bicomponent fiber which will not only increase the strength of the web, but also avoid the shedding problem associated with the outer portion of the fiber in carding machines.